Can't figure out where the buzz/sizzle is coming from

Apexpro

Greetings fellow Polkaphiles.

I've had a pair of SDA 2s I bought new in the 80s and recently purchased a pair of SDA 1Cs off Craigslist for $350. Maybe a little high I was thinking, but they were advertised as being in great condition, already recapped, and and the seller would deliver them. So I made the purchase.

We hooked them up to a big ole Luxman M300 to check them out and they sounded fine and looked to be in great shape. I knew they'd sound better when I hooked them up to my Threshold 400a Cascode (early Nelson Pass amp - 100wpc class A). And they did. But now when I crank it up with a heavy bass source media: Telarc's Micheal Murray playing Bach on the great organ at Methuen for instance or the first track on Weather Report's Heavy Weather I hear a buzz/sizzle out of the right channel during sustained low notes at high volume. I talked to the seller, a younger guy that was selling them for a friend, and he'd never heard the noise. But he'd also never driven them as hard as I have. He seems like a straight up young man and I have no reason to doubt him.

I've ruled out the amp - even at clipping levels there's no unpleasant noise coming from the SDA 2s or a 'Double Advent' setup I have. (yes, I hoard vintage bits)

At first I thought it was the lower 6511. I couldn't find one, but did find a new/old stock (2004) 6503 - after I read a thread here where it was recommended as an okay replacement.

But now I'm not sure. Before I started pulling things apart I decided 'one more listen to make sure you're pulling the correct driver'. And sure enough, I can't determine if it's one of the drivers or a harsh buzz from the passive radiator's metal surround, or ?. At lower volumes they sound really nice, tight bass, and definitely push some air. Everything is tight, no loose scews, cabinet is solid, etc.

Has anyone encountered anything like this before? And, if so, how did you determine the offender?

Thanks for your time!

Faustin

It could be even a cabinet wire vibrating against the passive inside the cabinet. I have a set of 1c's and when I opened them up a few months ago I made sure all of the wires were positioned away from things to prevent annoying little sounds. And FYI, after I purchased mine, I discovered that the guy I bought them from had several things wired wrong and had not removed the poly switch etc. Once I got everything straightened out and burned them in they have come alive. One other thing to check is the dust covers on the MWxxxx's. A week or so ago I noticed a funny noise from one of my 7's. Turns out that the dust cap was beginning to come off. It was only attached about 1/2 way and was vibrating now and then.

Apexpro

Thanks for the reply! Dust caps look good, so I guess it's time to crack things open and have a look-see. This "..could be even a cabinet wire vibrating against the passive inside the cabinet." could very well be the issue. My first thoughts were 'it can't be the passive - there's nothing to fry'. Since it only happens at house shaking levels I can wait until I get a set of "Larry rings" and clear a Saturday to get intimate with them.

Speaking of cracking, a joke a gal friend told me:

"What's the fastest way to a man's heart? A rib spreader."

Thanks again!

PolkieMan

No. MW6511. Is it the fabric sides coming loose? The recap, job look inside is everything secured? Are the inductors tied to the crossover board?

PolkieMan

Go ahead and order some spare drivers, sounds like you will need them.

Apexpro wrote: »

Thanks for the reply! Dust caps look good, so I guess it's time to crack things open and have a look-see. This "..could be even a cabinet wire vibrating against the passive inside the cabinet." could very well be the issue. My first thoughts were 'it can't be the passive - there's nothing to fry'. Since it only happens at house shaking levels I can wait until I get a set of "Larry rings" and clear a Saturday to get intimate with them.

Speaking of cracking, a joke a gal friend told me:

"What's the fastest way to a man's heart? A rib spreader."

Thanks again!

Apexpro

I've lost the context: "No. MW6511." - can I trouble you to expand on it a little pls?

The fabric looks really good. Small dent on one of the caps - would you recommend I attempt to pull it out or just leave it be? What's the best method to pull a dent? I've already tried a shop-vac and gaffer's tape with no results.

I don't have time today to look inside, but that's definitely the next move.

Apexpro

PolkieMan wrote: »

Go ahead and order some spare drivers, sounds like you will need them.

Aye. Always good to have spares. Is Polk's part dept. still the best place to get them?

westmassguy

Apexpro wrote: »

At first I thought it was the lower 6511. I couldn't find one, but did find a new/old stock (2004) 6503 - after I read a thread here where it was recommended as an okay replacement.

The 6503 is not a replacement for the 6511. The 03 is 8 ohm nominal, the 11 is 4 ohm

WastelandWand'r

My original M10's suffered at the hands of a fool (who was oftentimes drunk and stupid in college) who over drove them with a Denon Receiver. This fool also heard a buzzing sound coming during certain passages. It turned out that I had destroyed one of the tweeters. I felt around touching the edges of the drivers and tweets. If I pressed on the edge of the dome, the buzzing stopped. Maybe it has a fried tweeter and the dome is being excited. I know the laminate of the tweeters is a plasticky type material and sounded like a 'fizzy buzzy' (highly technical I know) sound.
If not, I hope that you are able to locate and fix it.
Enjoy them,
nathan

Apexpro

I may be confused - not an unusual state by any means. I've now seen two different diagrams for SDA 1C speaker placement. One says the 6511 is the 'outside' stereo driver and another says the 6510 is the 'outside' dimensional driver. By 'outside' I mean the right side of the right channel speaker / left side of left channel speaker.

I've also seen a list of Polk driver specs:

6503 6.54 Ohms 29 Hertz
6510 6.57 Ohms 31 Hertz
6511 3.13 Ohms 29 Hertz

What's correct?

Many thanks for your time!

Apexpro

Thanks Nathan! I'll get 'em fixed - once I figure out what the real issue is. Tomorrow will be disassembly day.

F1nut

The SDA driver(s) are always on the outside looking at the speakers from the listening position.

I've also seen a list of Polk driver specs:

6503 6.54 Ohms 29 Hertz
6510 6.57 Ohms 31 Hertz
6511 3.13 Ohms 29 Hertz

What's correct?

Yes, as westmassguy stated the 6503 is not a sub for the 6511.

As for your problem, pull the right channel PR. The spider may have separated from the foam.

Apexpro

Spider?

Very glad to hear the SDA drivers are on the outside, so if I have a driver issue it'll be a 6511. And I just found a pair on eBay for $60 w/ free shipping. Seller even mentioned he'd bubble wrap the heck out of 'em to avoid magnet movement in case of rough handling.

Thanks to everyone that's offered up their time and knowledge.

Apexpro

btw F1nut - Is it possible you're a Formula 1 devotee DeadHead like myself?

F1nut

Pull the PR, look at the back end. You'll see a Styrofoam piece, which should be glued to a round paper looking piece. If they have separated, that's your problem.

Yes, I'm a rabid Formula 1 fan. Not really a Deadhead though as I only like the first 3 albums, but I did see them 9 or 10 times way back when.

Apexpro

F1nut wrote: »

Pull the PR, look at the back end. You'll see a Styrofoam piece, which should be glued to a round paper looking piece. If they have separated, that's your problem.

Yes, I'm a rabid Formula 1 fan. Not really a Deadhead though as I only like the first 3 albums, but I did see them 9 or 10 times way back when.

It's been a great season so far; some of the best races I've seen in years. Even the 'silly season' is sillier than ever. But I digress.

Thanks for the explanation. I thought my son was coming over today to help me move the 1Cs to a work spot but he needed to take advantage of the good weather - so we'll get to it one evening this week. I'll report back with what I find.

Did pick up a nice amp at a great price today - one with enough guts to bring these 1Cs totally alive.

Apexpro

Ok, I'm trying to get everything I might need together in one place before I start taking things apart. Is Aleene's Tacky Glue still the recommended adhesive for gluing the Styrofoam & spider back? What's best for resealing drivers to the cabinet? Same?

I've managed to scrounge up a couple of 6510s for $30 a piece from a gentleman in Miami. They arrived today and appear to be in excellent condition.

Is a .5 ohm resistor still the recommended replacement for the polyswitches? (I'm digging through threads but some are older than my ties, so just checking).

I'm so jazzed to finally have a set of 1Cs I bought a 'new to me amp' just for them.

My plan is to listen to them for a while as is so I can fully appreciate the hotrodding that'll inevitably happen.

F1nut

Is Aleene's Tacky Glue still the recommended adhesive for gluing the Styrofoam & spider back?

Something newer, Loctite Power Grab.

What's best for resealing drivers to the cabinet? Same?

If the original gaskets are not ripped/torn, do nothing. If one or more is damaged you can replace the original Armacell.

Is a .5 ohm resistor still the recommended replacement for the polyswitches?

Generally speaking, yes. Some prefer a .22. Let your ears decide.

westmassguy

Loctite might be a little difficult to work with between the spokes of the basket frame. Aleen's is what I use for that type of repair. Get a 1/4" wide artist's brush, and squirt a little Aleen's in a cup, then "paint" it wherever the repair is needed. The Loctite has a gel quality to it, the Aleen's is more fluid.

Apexpro

What wattage on the resistor? I'm a nuts and bolts kinda guy - this is my first DIY electronics project.

westmassguy

Mills MRA-12 from Parts Express or Soniccraft. You can also go with Mundorf MOX 10 Watt from Madisound.

Apexpro

Thanks all!

Apexpro

After checking everything suggested, swapping out drivers, cleaning connections, etc. I'm still getting the ugly noise. Focus has changed to the amp. It's a Threshold 400a Cascode and to the best of my knowledge has never been touched. At least not in the last 10 years. Time for a refurb/update.

I have another amp on the way, will swap it out, and if I still have the noise I'm assuming the only thing left is the crossover circuit. Since I'm not qualified to test/repair the crossover it will go to my tech.

I sincerely appreciate everyone's time and knowledge sharing. I'm overwhelmed with the immediate attention and kindness with which everyone has bestowed on me. I'll continue to lurk around and will post the final solution.

Thanks everyone!

westmassguy

If it is the amp, try swapping the left and right speaker wires. If the problem moves to the other speaker, it's most likely the amp.

Apexpro

Since I'll have another SS amp arriving this week I'm waiting to hook it up. I don't want to risk damaging the speaker or the Threshold amp at this point. I'll let everyone know the outcome so we can put this thread to bed.

Apexpro

Daughter just called me from home - the amp has arrived. Will let it warm up tonight and tomorrow we should know the answer to this question.

Apexpro

Ok. I'm now thinking demonic possession.

Both pairs of my SDAs pop/sizzle at next to insane levels with different amps. Right at the clipping level for the Threshold, but way shy of what the MAC2205 will drive. If I switch speakers the sound issue remains with the right channel on both the SDA 2s and the 1Cs. I'm baffled.

Is it possible I may need to 'burn in' the speakers? For a decade or more I've had the balance more to the left because of the layout of the room (I know - change the room to suit the speakers). I don't think the 1Cs have ever been driven as hard as I'm driving them.

I'm pretty confident in saying the issues lies with the right channel speaker since the noise follows it - and it's the same for both pairs. Which is weird. Any ideas?

Maybe I need new wires? ;-} ....ok, sorry, promised not to go there. I'm having a laugh at my own expense - pls feel free to join me, I can take a lashing without losing my sense of humor.

westmassguy

Pops and sizzles are definitely not normal. It sounds like you've already cooked something.

F1nut

Your amps, are they common ground?

Apexpro

nbrowser wrote: »

Ok, different amps, swapping speakers, now I'd start looking at the preamp/processor as having a fault in it, got another preamp to test with?

I've tried with different pre-amps. The MX-113 in the back room and the Parasound in the main room. Perhaps I have already cooked something. It may be I'm asking too much of everything. The source media (Telarc - Murray - Bach, Great Organ at Methune) will make it happen every time when it's cranked up to ear bleed levels. But Joe Satriani live DVD, Radio Kaos, Aja, all really loud and no bad noises. I can play pretty much anything at lower levels without nastiness.

Everything sounds really great with the new (to me) MC2205 - big difference in the way the 1Cs sound at all levels. Crisp, warm, powerful. I think I just need to stay away from deafening levels.

Apexpro

F1nut wrote: »

Your amps, are they common ground?

Yes, both are common ground in stereo mode.